In general, as ink-jet recording apparatuses that flexibly respond to high-mix, low-volume demands, conventionally, ink-jet type ink-jet recording apparatuses are known. An ink-jet type ink-jet recording apparatus jets ink from nozzles provided on a surface of the recording head, the surface facing a recording medium, so that the ink impacts and fixes onto the recording medium, and thereby an image is recorded on the recording medium.
Recently, as ink-jet recording apparatuses applicable to various recording media, ink-jet recording apparatuses using photocurable type ink are known (for example, refer to Patent Document 1 and Patent Document 2). Each of these uses photocurable ink containing a photoinitiator having a predetermined sensitivity to light, and ink having impacted onto the recording medium is exposed to light, thus the ink is cured to be fixed on the recording medium. By such an ink-jet type ink-jet recording apparatus using photocurable ink, ink is instantly cured just after having impacted on to the recording medium and been exposed to light. Therefore, ink sinks into the recording medium or blots little, making it possible to record an image, not only onto a plain paper sheet, but also onto a recording medium of a material such as plastic-or metal, which does not absorb ink at all.
Such an ink-jet recording apparatus using photocurable ink requires jetted ink to be exposed to light of an intensity that is great enough to properly cure and fix the ink. To meet this requirement, in recent years, there has been offered cation-curable ink that accumulates energy and can be cured by exposure to light of even low illumination intensity if the exposure is performed for a long time. To cure this cation-curable ink, a low-pressure mercury lamp or an ultraviolet light source of a low electric power and low output power, such as a cold-cathode tube, can be utilized. Even in the case of using such an energy accumulating ink, it is required that an UV-ray light source can emit light which can properly cure and fix the ink. To enable this, it has been offered that a specific light intensity required for curing the ink is obtained by increasing the electric power to be supplied to the light source and thus increasing the emission intensity per unit time of the light.
[Patent Document 1] TOKKAI No. 2001-310454
[Patent Document 2] TOKKAI No. 2003-145725
However, when emission intensity is increased, the amount of heat generation by the light source is also increased. Especially, the light emission efficiency of a low-output type light source depends on the temperature of the metal cap, of the light source, that discharges electricity and has a characteristic of dropping in light emission efficiency at a too high temperature of the metal cap, and thus the low-output type light source has a problem of difficulty in stably maintaining a light emission efficiency preferable for curing ink. To prevent curing of ink adhering to a nozzle formed surface of a recording head, wherein the curing of ink could occur when light having emitted by the light source reaches the nozzle formed surface, and to prevent a harmful effect, on human health, of leakage of light having been emitted from the light emitting device, the light emitting device is conventionally provided with a cover member or the like that covers the-light source. Accordingly, heat generated by lightning of the light source stays in the space covered by the cover member and the temperature there rises, thus, the temperature of the metal cap rises, and thereby a problem of drop in light emission efficiency of the light source is caused. Particularly, in the case of increasing the emission intensity by arranging a plurality of light sources of a line-tube type, since the metal caps of the light sources are near each other, the metal caps of the light sources located near the central part cause thermal interference to each other, making the problem of drop in light emission efficiency of the light sources more significant.
Therefore, conventionally, consideration has been made on cooling a metal cap with water or the like to maintain the temperature of the metal cap at a constant value. However, in the case of a light source of line-tube type, since metal caps are provided at both ends of a light emitting tube, when a plurality of light sources are provided, in order to water cool the metal caps of all the light sources, it is required to provide a mechanism or the like for circulating cooling water widely on both sides of a light emitting device provided with metal caps, causing a problem of complication and large size of an apparatus to be manufactured.
Further, since a light source is degraded as it is used, it is necessary to properly replace the light source. In the case where an apparatus is provided with a plurality of light sources of a line-tube type, a water cooling mechanism as described above is provided. Accordingly, there is also a problem of requiring painstaking works including replacement of light sources.
Still further, electronic radiation material (emitter) coated on a filament of a metal cap spatters by repeated flickering of a light source, and thereby proceeds blackening of the vicinity of the electrode of the metal cap. As the blackened region grows, the light emission intensity of the vicinity of the metal cap of the light source gradually drops. Thus, in the case of a line tube type, it is possible that a blackened region grows in the entire light emitting tube with elapsed time from when the light source started burning, causes unevenness of the emission intensity of the light source, and disables curing of ink with evenness.